Re: [PATCH 2/2] kbuild: Disable CONFIG_LD_ORPHAN_WARN for ld.lld 10.0.1

[Nathan Chancellor]

On Tue, Nov 17, 2020 at 11:41:15AM -0800, Nick Desaulniers wrote:
> On Fri, Nov 13, 2020 at 11:56 AM Nathan Chancellor
> <natechancellor@xxxxxxxxx> wrote:
> >
> > ld.lld 10.0.1 spews a bunch of various warnings about .rela sections,
> > along with a few others. Newer versions of ld.lld do not have these
> > warnings. As a result, do not add '--orphan-handling=warn' to
> > LDFLAGS_vmlinux if ld.lld's version is not new enough.
> >
> > Reported-by: Arvind Sankar <nivedita@xxxxxxxxxxxx>
> > Reported-by: kernelci.org bot <bot@xxxxxxxxxxxx>
> > Reported-by: Mark Brown <broonie@xxxxxxxxxx>
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1187
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1193
> > Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> > ---
> >  MAINTAINERS            |  1 +
> >  init/Kconfig           |  6 +++++-
> >  scripts/lld-version.sh | 20 ++++++++++++++++++++
> >  3 files changed, 26 insertions(+), 1 deletion(-)
> >  create mode 100755 scripts/lld-version.sh
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 3da6d8c154e4..4b83d3591ec7 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -4284,6 +4284,7 @@ B:        https://github.com/ClangBuiltLinux/linux/issues
> >  C:     irc://chat.freenode.net/clangbuiltlinux
> >  F:     Documentation/kbuild/llvm.rst
> >  F:     scripts/clang-tools/
> > +F:     scripts/lld-version.sh
> >  K:     \b(?i:clang|llvm)\b
> >
> >  CLEANCACHE API
> > diff --git a/init/Kconfig b/init/Kconfig
> > index a270716562de..40c9ca60ac1d 100644
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -47,6 +47,10 @@ config CLANG_VERSION
> >         int
> >         default $(shell,$(srctree)/scripts/clang-version.sh $(CC))
> >
> > +config LLD_VERSION
> > +       int
> > +       default $(shell,$(srctree)/scripts/lld-version.sh $(LD))
> > +
> >  config CC_CAN_LINK
> >         bool
> >         default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag)) if 64BIT
> > @@ -1349,7 +1353,7 @@ config LD_DEAD_CODE_DATA_ELIMINATION
> >           own risk.
> >
> >  config LD_ORPHAN_WARN
> > -       def_bool ARCH_WANT_LD_ORPHAN_WARN && $(ld-option,--orphan-handling=warn)
> > +       def_bool ARCH_WANT_LD_ORPHAN_WARN && $(ld-option,--orphan-handling=warn) && (!LD_IS_LLD || LLD_VERSION >= 110000)
> >
> >  config SYSCTL
> >         bool
> > diff --git a/scripts/lld-version.sh b/scripts/lld-version.sh
> > new file mode 100755
> > index 000000000000..cc779f412e39
> > --- /dev/null
> > +++ b/scripts/lld-version.sh
> > @@ -0,0 +1,20 @@
> > +#!/bin/sh
> > +# SPDX-License-Identifier: GPL-2.0
> > +#
> > +# ld.lld-version ld.lld-command
> 
> ^ it looks like this format was copied from scripts/gcc-version, but
> it's kind of curious/cryptic to me for a comment about usage.  Is it
> necessary?  A comment in the form:
> 
> # Usage: ./scripts/lld-version.sh ld.lld
> 
> Would be clearer to me.
> 
> > +#
> > +# Print the linker version of `ld.lld-command' in a 5 or 6-digit form
> > +# such as `100001' for ld.lld 10.0.1 etc.
> > +
> > +linker="$*"
> > +
> > +if ! ( $linker --version | grep -q LLD ); then
> > +       echo 0
> > +       exit 1
> > +fi
> > +
> > +VERSION=$($linker --version | cut -d ' ' -f 2)
> 
> This is going to invoke the linker potentially twice if it's LLD.
> Would it be nicer to capture the output of `$linker --version`, check
> which linker it is, then slice that up via `cut` to get the version?
> 
> This version is fine to me, but if you're going to send a v2, that
> might be a nice slight cleanup.  Otherwise,
> 
> Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> 
> (Please drop those tags if you modify this for v2 and I'll rereview/retest).

Below is the impending v2 if you wanted to give it an early test, I plan
to send it along formally Thursday morning with all of the addressed
feedback so far.

Cheers,
Nathan

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